Scroll down to "Lose yourself in surround sound" with the picture of the dolby USB dongle. You will see a hyperlink that says "download the latest drivers here." Be sure to read the readme if you are updating.
Follow jlee14's link, that download is the only driver I was able to even extract. Downloaded as the same .zip, which I thought was strange. This last one was the third .zip(3) time, first two also from sennheiser website, but showed as corrupt.
Not the support I would expect from a $300(msrp) headset.
Absolute INCREDIBLE sound quality and comfort though! =]